The Protein Expression Laboratory (PEL) at the National Cancer Institute (NCI) - Frederick assists NCI and NIH investigators in the cloning, expression, and purification of proteins important in human disease, and develops new protein technologies. For this purpose, PEL comprises five groups: Clone Optimization; Molecular Fermentation; Eukaryotic Expression; Protein Purification; and Protein Technologies. Together or individually, these groups can speed the process of obtaining clones and proteins, thus making NCI staff more efficient and productive. PEL seeks to acquire or develop the most advanced capabilities possible for the benefit of its users. Our staff consults with each investigator to determine the most appropriate technology to apply to particular research tasks. Our experience assisting dozens of NCI researchers allows us to improve the likelihood of success for each new project. The Clone Optimization Group (COG) constructed over 600 entry and expression clones for investigators (see Table I) in FY2007. Many of these were tested for expression in combinations of different organisms (bacterial, insect, mammalian, yeast), culture conditions, and fusion tags. Much of the cloning and subcloning was done using Gateway in vitro recombination. COG maintains a large collection of Gateway destination vectors. The Molecular Fermentation Group (MFG) provides small-, intermediate-, and large-scale fermentation of recombinant bacteria and yeasts for investigators from a wide cross-section of the research community at NCI Frederick and NIH-Bethesda. State-of-the-art minifermenters yield 3 to 10 times as many cells at costs similar to shake flasks. Strains are constructed and verified for productivity prior to scale-up using SDSPAGE and Westerns. The MFG monitors cell density, dissolved oxygen, methanol, glucose, and other metabolites and uses these data to control culture conditions for maximum yield and protein quality. The Eukaryotic Expression Group (EEG) provides technical expertise and production of cells and cellderived products in support of NCI, NIH, and SAIC Frederick, Inc., investigators. Major products and services include monoclonal antibodies (MAb), cytoplasmic and secreted recombinant proteins from transfected mammalian cells or the baculovirus insect cell expression vector system, bulk cells, cell banking capabilities, and partial purification of manufactured products.